How to examine and sample a soil profile?

Soil is a non-renewable natural resource vital for our existence. Soil produces 98.7% of the calories consumed by humans globally, holds more organic carbon in the surface 3 meters than the atmosphere and vegetation combined, and is home to 59% of the species on Earth, making it critical for global biodiversity (Kopittke et al., 2025). 

Soil Scientists study the soil using the soil profile. Soil profile, the vertical section of the soil from the surface to the bedrock below, is the basic unit of soil examination and sampling. A soil profile consists of soil layers called soil horizons. The characteristics of soil horizons depend on the dominant soil processes. They are influenced by soil-forming factors such as climate, relief (topography), organisms (vegetation, soil organisms, human activities, etc.), parent material (types of rocks), and time (duration of soil formation). 

A soil profile of Faraon clay, developed from limestone, in Baybay, Leyte.

To examine a soil profile, a pit measuring 1m x 1m to a depth of at least 1.5m (or to the bedrock or water table) is excavated. Recent road cuts and landslide faces generally offer good opportunities to examine and sample soil profiles. Soil profiles are examined and described using standard procedures. The global standard reference is the book “Guidelines for Soil Description” (4th edition), published by the Food and Agriculture Organization (FAO) of the United Nations in several languages. The book was co-authored by Reinhold Jahn (Martin Luther University, Germany), H.P. Blume (Kiel University, Germany), Victor B. Asio (Visayas State University, Philippines), Otto Spaargaren (ISRIC, Netherlands), and Peter Schad (Technical University Munich, Germany). 

The Guidelines for Soil Description published by FAO & its authors.

After the soil profile has been evaluated and described, approximately 1 kilogram of soil is collected from each soil horizon for laboratory physical, chemical, mineralogical, and biological analyses. The old and widespread practice is to collect 3 or more subsamples from each horizon and then mix them into a single representative sample for that horizon. 

A better method is the quantitative soil profile sampling method (or the Hohenheim soil profile quantitative sampling method) developed in the 1960s by Ernst Schlichting, the renowned professor and director of the Institute of Soil Science and Site Ecology at the University of Hohenheim, Stuttgart, Germany. The said sampling method was introduced in the influential book “Bodenkundliches Praktikum (Soil Science Practicum)” by Ernst Schlichting and his assistant, Hans-Peter Blume. 

Due to its widespread use in German-speaking countries, the book was revised by his former students, H.P. Blume and Karl Stahr, and published as 2nd edition in 1995. In 2011, the 3rd edition was published and authored by H.P. Blume, K. Stahr, and P. Leinweber. 

H.P. Blume, K. Stahr, and P. Leinweber are now retired professors of soil science at the University of Kiel, University of Hohenheim, and University of Rostock, Germany, respectively. H.P. Blume and K. Stahr were presidents of the German Society of Soil Science.

References

Kopittke, P. M., Harper, S. M., Asio, L. G., Asio, V. B., Batalon, J. T., Batuigas, A. M. T., ... & Sanchez, P. B. (2025). Soil degradation: An integrated model of the causes and drivers. International Soil and Water Conservation Research.

Schlichting, E. and Blume, H.P. (1966). Bodenkundliches Praktikum (Soil Science Practicum). Verlag Parey, Hamburg. 

Schlichting, E. Blume, H.P., and Stahr, K. (1995). Bodenkundliches Praktikum (Soil Science Practicum)(2. Auflage). Verlag Blackwell, Berlin.

Cuatro Islas in Leyte: The pristine tropical paradise

 Protected Landscape/Seascape 

The four islands collectively known as the Cuatro Islas—Apid, Digyo, Himokilan, and Mahaba—were proclaimed on April 23, 2000, as a protected landscape/seascape under the NIPAS Act of 1992 by President Joseph Ejercito Estrada through Proclamation No. 270. The protected area is under the administrative jurisdiction of the municipalities of Inopacan and Hindang, Leyte.

Location of Cuatro Islas off the coast of Inopacan and Hindang, Leyte

 Geologic Origin 

The Cuatro Islas are believed to be remnants of a barrier reef system located off the coast of Inopacan and Hindang in Leyte. In a study conducted during the International Tropical Ecology Workshop in 1999 organized by the ViSCA-GTZ Tropical Ecology Program, we proposed that these coral reef islands are underlain by a volcanic basement connected to the extinct Mt. Sacripante on the Leyte mainland (Grenz et al., 1999). Geological evidence suggests that the islands formed during the Upper Pleistocene epoch of the Quaternary period, as indicated by the presence of coralline limestone of Quaternary age. During the Last Glacial Maximum, approximately 15,000 years ago, sea levels across Southeast Asia dropped by about 100 to 150 meters. This significant decline exposed large portions of the continental shelf, creating conditions favorable for coral growth in newly formed shallow tropical marine environments. In addition, ongoing tectonic uplift in Leyte and other parts of the Philippines further facilitated reef development, as corals thrive in shallow, sunlit warm waters. This combination of falling sea levels and gradual tectonic uplift contributed to the emergence and present configuration of the barrier reef system. Similar uplifted coral reef formations can also be found in the northwestern and southwestern regions of Leyte Island (Grenz et al., 1999). 

Digyo Island, a pristine tropical paradise

 Digyo, the Jewel of the Cuatro Islas 

 Among the four islands, Digyo stands out for its relatively flat, low-lying topography, rising only about 2 to 3 meters above the present sea level. It suggests that Digyo is geologically younger than the other islands, having formed more recently. Its crystal-clear turquoise water and fine white sand, derived from coralline limestone and the shells of marine organisms, make Digyo a favorite destination for tourists. Many people call it the jewel of the Cuatro Islas. 

The stunning white sandbar 

 Digyo Soils are Sandy and Undeveloped 

 The soils of Digyo Island are dominated by sand (largely calcium carbonate) and show no signs of pedogenesis. Roots of coconut trees, the main vegetation on the island, hold the sandy soil but contribute little humus. The soils belong to the Entisols order in Soil Taxonomy, and Arenosols in the World Reference Base (WRB). 

The young, sandy, & undeveloped soil of Digyo Island showing roots of coconut trees

Photo credit: All photos were taken by V.B. Asio on 25 April 2026

 

Reference 

Grenz, J., Zukunft, S., & Asio, V. B. (1999). Geomorphology and soils of Apid Island, Inopacan, Leyte, Philippines. Annals of Tropical Research, 21, 1-8.

Soil Health Concept and Initiatives in the Philippines

What is Soil Health? 

Although not yet clearly defined, soil health has become a widely used term globally, even beyond the scientific community. This may be because the term “health,” defined by the Cambridge Dictionary as “the condition of the body and the degree to which it is free from illness, or the state of being well,” is easily understood by many people. By humanizing the condition of soil through the term “soil health,” issues such as soil degradation become more accessible and easier to understand for individuals from diverse backgrounds. 

A "healthy soil" used for intensive vegetable production in Cabintan, Ormoc, Leyte

Zethof et al. (2026) noted that the current popularity of soil health is unparalleled in the field of soil science. However, they question whether the term is merely a clever marketing strategy or if it has the potential to advance soil science beyond simple popularization. 

The Food and Agriculture Organization (FAO) has reported that the concept of a “healthy soil” has not yet been officially defined, despite being widely used for more than a decade. Soil health generally refers to the performance or functioning of soil, rather than its intrinsic physical, chemical, or biological properties. The Intergovernmental Technical Panel on Soils (ITPS) defines soil health as “the ability of the soil to sustain the productivity, diversity, and environmental services of terrestrial ecosystems.” 

A "sick soil" (unhealthy soil) due to salinity (seawater intrusion) in Matalom, Leyte

Soil health evolved from earlier, more technical terms such as soil quality and soil fertility. Soil quality is one of the three components of environmental quality, alongside water and air quality. While water and air quality are primarily defined by levels of pollution affecting human and animal health or natural ecosystems, soil quality is broader. It is defined as “the capacity of a soil to function to sustain biological productivity, maintain environmental quality, and promote plant and animal health” (Bünemann et al., 2018). In his book Pedologie oder allgemeine und besondere Bodenkunde, F.A. Fallou, one of the founders of soil science, introduced the term soil quality (Qualitas), although with a different meaning (Asio, 2005). 

A sick soil due to high acidity (soil pH below 4.5) in Quinapondan, Eastern Samar

Furthermore, soil fertility originated from the German term “Bodenfruchtbarkeit” and focuses primarily on crop production. According to the FAO, soil fertility is “the ability of the soil to supply essential plant nutrients and soil water in adequate amounts and proportions for plant growth and reproduction, in the absence of toxic substances that may inhibit plant growth.” 

Soil Health Initiatives in the Philippines 

In the Philippines, the National Soil Health Initiatives are being championed by Congressman Adolph Edward “Eddiebong” G. Plaza, the 2nd District Representative of Agusan del Sur. His soil health initiatives focus on several key areas, including the formulation of a national soil health strategy and the implementation of a “From Lab to Land” approach. This approach promotes the use of advanced soil testing laboratories and modern technologies, such as drones, to monitor soil moisture, fertility, and erosion risks. It also encourages crop diversification and land rehabilitation. 

Congressman Eddiebong Plaza addressing the participants of the Stakeholders' Forum
he organized on Dec 3-5, 2025

Congressman Plaza’s partners and collaborators include ACIAR-SLAM (Dr. Johnvie Goloran), Griffith University (Prof. Chengrong Chen), DOST-PCAARRD, the Department of Agriculture–Bureau of Soils and Water Management (DA-BSWM), Agusan del Sur State University (ADSSU; Pres. Joy Capistrano), Southern Leyte State University–Hinunangan (SLSU-Hinunangan; Dr. Ian Navarrete), and the Society for the Advancement of Philippine Soil Science (SAPSS; Dr. VB Asio). 

In support of this initiative, Congressman Plaza organized the Stakeholders’ Forum on Soil Testing Protocols and Information Systems, held on December 3–5, 2025, in Prosperidad, Agusan del Sur. 

References 

Asio, V. B. (2005). "Comments on" Historical development of soil and weathering profile concepts from Europe to the United States of America"." Soil Science Society of America Journal 69: 571-572.

 Bunemann, E. K., Bongiorno, G., Bai, Z. G., Creamer, R., De Deyn, G. B., de Goede, R. G. M., ... & Brussaard, L. (2018). Soil quality-A critical review. Soil Biology and Biochemistry, 120, 105-125. 

Zethof, J. H., Kalbitz, K., & Jungkunst, H. F. (2026). Soil Health—What Is It Good for?. Journal of Plant Nutrition and Soil Science.

The rock formation along the highway in San Jose, Dulag, Leyte

Have you ever wondered about the rock along the highway in San Jose, Dulag, Leyte? Especially where the road runs close to the sea, travelers see a striking, dark-colored rock formation exposed by the ongoing road widening. 

The andesite rock along the highway in San Jose, Dulag, Leyte

Formed by volcanism between 2.6 and 23 million years ago during the Miocene and Pliocene epochs, this rock in Dulag is known as andesite. Andesite is an intermediate type of volcanic rock, with silica (SiO2) content ranging between 52% and 63%, commonly found in areas with past or present volcanic activity. 

The Dulag andesite belongs to the Pliocene-Miocene intermediate rocks (Jahn & Asio, 2006)

Andesite got its name from the Andes Mountains in South America, where it is abundant. It is also widespread in volcanic regions around the world, especially along the Pacific Ring of Fire, where many volcanoes produce this type of rock. It is an extrusive (volcanic type) and the most widespread igneous rock in the Philippines. 

Andesite typically appears fine-grained, sometimes with small visible crystals embedded in it called phenocrysts. These crystals are often made of minerals like feldspar and dark-colored minerals such as pyroxene or biotite. Because of this, andesite can look gray, pinkish, or slightly dark, depending on its composition. 

Mineral composition of the andesite in Abuyog: Amp- amphibole; Cpx- clinopyroxene;
Opq-opaque minerals; Pl-plagioclase feldspar

Laboratory examination of thin sections using a petrographic microscope (above photo) revealed that the andesite in Dulag, Leyte, consists primarily of plagioclase feldspar (45% of the mineral content), clinopyroxene (20%), and amphibole (5%), along with minor amounts of secondary minerals. It is darker in color compared to the younger andesite rocks (Quaternary volcanics) in the central highlands of Leyte.

The typical andesite rock in the central highlands of Leyte formed by volcanism during the Quaternary period (2 million years ago up to the present). The sample comes
from Cabintan, Ormoc at an elevation of 900 m above sea level.

Acknowledgement

I thank the National Institute of Geological Sciences (NIGS) at UP Diliman for conducting the thin section analysis of my rock samples.

References

Britannica Editors. "andesite". Encyclopedia Britannica, 5 Jul. 2015, https://www.britannica.com/science/andesite. Accessed 3 April 2026.

Jahn, R., & Asio, V. B. (2006). Climate, geology and soils of the tropics with special reference to Southeast Asia and Leyte (Philippines). In Proceedings of the 11th International Seminar-Workshop on Tropical Ecology (pp. 21-25).

The Rock, Mineral, and Soil Collection at VSU: An essential Instructional Resource

The Rock, Mineral, and Soil Collection at the Pedology and Geoecology Laboratory of the Department of Soil Science, Visayas State University, Baybay City, is a popular educational attraction for students in Eastern Visayas. It contains hundreds of specimens, including different types of rocks (igneous, metamorphic, sedimentary), minerals (e.g. quartz, feldspar, calcite, amethyst, jade, jasper, mica, pyrite, etc), as well as sands and soils collected from different places in the Philippines and abroad. It is the only one of its kind in the Visayas and Mindanao.

In 2026, new additions to the collection include red sandstones from Utah (USA), peridotite and andesite rocks from Eastern Samar and Southern Leyte, and various mineral specimens donated by some alumni of the department.

Soil samples from across the Philippines are also on display. The collection is an essential resource for the teaching of soil science, agricultural science, environmental science, and earth science. Most soils (except peat soils) originate from weathered rocks, and the mineral composition of these rocks strongly affects soil properties and fertility. Rocks also serve as a source of nutrients that are gradually released into the soil through weathering.

A few of the many igneous rocks in the collection

Some of the metamorphic rocks on the display in the collection

Some samples of sedimentary rocks in the collection

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Note: The Rock, Mineral, and Soil Collection was established and is maintained by Dr. V.B. Asio. For more information or if you want to visit it, please email him at: vbasio@vsu.edu.ph

Landslides changed the soil characteristics in Leyte, Philippines

By Maria Cristina A. Loreño & V.B. Asio 

Landslide is defined as the downslope movement of soil mass, rocks, and debris. It is one of the most serious environmental hazards in the Philippines. On April 11, 2022, four catastrophic landslides occurred in Leyte due to tropical storm Agaton, which caused the loss of hundreds of human lives (for a detailed explanation of the causes, please see the Soil and Environment blog). Two of the landslides happened in Bunga and Mailhi in Baybay City. Until now, little research has been done on the effects of landslides on soil properties and soil development. Such information is crucial for the rehabilitation of landslide-affected areas. The objective of the study was to evaluate the changes in the morphological, physical, and chemical properties of volcanic soils due to landslides. 

The study was conducted in the Bunga landslide with old soil (Ultisol) and in the Mailhi landslide with young volcanic soil (Andisol). The sites are found on steep volcanic mountain slopes underlain by andesitic pyroclastic rocks. Vegetation in both sites is a mixture of trees, coconuts, and shrubs. Soil profiles were examined and sampled on the upper, middle, and lower portions of the landslides. The soil profiles on the upper slopes were not affected by the landslides and were used as reference (unaffected soil). Soil samples were collected from every soil horizon or layer and analyzed in the laboratory for physical and chemical properties.

 

Results revealed that the landslides changed many soil characteristics crucial to soil use and productivity. In particular, the kind and depth of soil horizons, soil color, abundance of plant roots, and presence of rock fragments were modified by the landslides. The trend was the same for both the old and young soils (Figs. 1&2). In Bunga with old soil, the landslide resulted in more clayey soil but with very irregular distribution with soil depth. In Mailhi, with young soil, the landslide led to the increased sand content in the soil profile (Fig. 3). 

Figure 1. Changes in soil morphology due to landslide in Mailhi, Baybay 

Figure 2. Changes in soil morphology due to landslide in Bunga, Baybay

Figure 3. Changes in the sand, silt, and clay contents with soil depth due to landslides.

As expected, landslides increased the soil's porosity due to the mixing and deposition of soil material. In terms of soil pH, the landslides increased the pH of both the old and young soils due to the mixing of the soil and the deposition of fertile topsoil from the upper slopes (Fig. 4). Landslides tended to decrease the soil organic matter (SOM) in the topsoil but increased it in the subsoils (Fig. 5).

Figure 4. Changes in soil porosity and pH due to landslide.

Figure 5. Changes in soil organic matter content with soil depth due to landslide.

Landslides changed the characteristics of the soils and the degree of soil development. The mixing of the soil made the soil unstable and prone to soil erosion and further slope failure. The landslides also lowered the fertility and potential productivity of the soils. Because of the instability of the soils, a few years should be allowed to pass before the landslide sites are utilized for agriculture, forestry, or other land uses.

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Note: This article is based on the poster presented by the authors at the 12th ASTHRDP Graduate Scholars Conference organized by the DOST-SEI and the National Science Consortium on 12-13 September 2024 at the Dusit Thani Resort Mactan, Lapu-Lapu City, Cebu. We thank the DOST-SEI for the ASTHRDP scholarship to MCAL and Dr. Luz Geneston Asio, and Mr. Kenneth Oraiz, GAC Members, for their valuable comments.

Some notes on the soils in the vegetable landscape of Benguet, Northern Luzon

Soils are formed from the weathering of rocks as influenced by climate, parent rock, topography, living organisms, and time. Among these factors, climate and topography appear to be the dominant factors that have influenced the properties and distribution of soils in Benguet, Northern Luzon. 

Benguet together with Abra, Apayao, Baguio City, Ifugao, Kalinga, and Mountain Province comprise the Cordillera Administrative Region (CAR). Benguet has a mountainous topography consisting of peaks, ridges, and canyons ranging in elevation from about 900m to 2,840m above sea level. 

The highest point of the Philippine highway in Cattubo, Atok, Beneguet

The subtropical highland climate (Cwb based on Köppen climate classification) with annual average highs of 25.3 °C in April and lows of 13.3 °C in January and an average precipitation of 1,829mm (Wikipedia) promotes moderate rock weathering and soil formation rates. The steep slopes on most mountain sides enhances rapid leaching and runoff, the latter results in severe soil erosion on cultivated and bare slopes. 

Steep slopes with young soils are terraced and planted to various vegetables

Most soils in Benguet have developed from diorite, an intermediate plutonic rock, as well as metavolcanics and metasedimentary rocks particularly slate. According to the published literature, the dominant natural vegetation of Benguet was the pine forest type. Compared with broadleaf forests, pine forests have lower soil organic carbon (SOC) contents, smaller labile carbon fractions, and lower amounts of SOC stocks. Moreover, pine forests tend to experience severe water erosion events (Nie et al., 2019. Catena 174: 104-111).

Outcrops of metasedimentary rocks in Atok, Benguet

The high soil erosion rates result in poorly developed and thin soils (Inceptisols). On more stable surfaces such as on summit positions, old soils can be found which may qualify as Ultisols. Regardless of the stage of soil development, most soils are acidic with pH below 5.0 (Laurean et al., 2015. Benguet State University Research Journal 74: 10-34).

Red and old soils on summit positions in the mountains.

Where intensive vegetable production is found, the landscape can be called Anthropocene landscapes due to the considerable soil and landscape modification resulting from human activities such as land use conversion from forest to agriculture, terracing, fertilizer and pesticide application, liming and others.

The beautiful Anthropocene vegetable landscape in Natubling, Buguias, Benguet.

In general, the rates of fertilizer and lime application by the vegetable farmers are not based on recommended rates. This necessitates soil fertility assessment of vegetable farms to be able to determine the appropriate rates of fertilizer and lime application for improved vegetable production. This is one of the objectives of our ACIAR SlAM Project (2020117) on managing heavy metals and soil contaminants in vegetable production led by Dr. Steve Harper of the University of Queensland, Australia.

Our ACIAR Slam Project Team from the Univ Queensland, UPLB, BSU, VSU & USTP